Which two label-distribution methods are used by MPLS routers?

MPLS routers use two primary label-distribution methods: downstream unsolicited and downstream on demand. In downstream unsolicited mode, a Label Switching Router (LSR) advertises labels for its directly connected routes and routes learned from other protocols to its peers without being explicitly requested. This is the default and most common method, offering faster label distribution. In downstream on demand mode, an LSR only advertises a label for a specific FEC (Forwarding Equivalence Class) when an upstream LSR explicitly requests it. This conserves resources but can be slower. LDP discovery hello messages and targeted hello messages are used for neighbor discovery and session establishment, not label distribution itself. LDP session protection messages are for maintaining session integrity.